A ski generally comprises a lower sliding surface having an angle iron on each lateral side edge for engaging snow, two lateral side surfaces defining the width of the ski, and an upper surface having means, located in a central or binding zone, by which a user attaches his foot to the ski. The leading end of the ski is usually curved upwardly in the form of a spatula; and the ski is relatively narrow in width compared to its length which defines a longitudinal direction.
In conventional skis, the thickness of the body of a ski varies along the length of the ski in the longitudinal direction, having a maximum in the binding zone where the flexional moments are generally greatest during use of the ski. Because the thickness of the ski near its central zone is a maximum, and the thickness near each of the front and rear ends of the skis a minimum, a uniform load distribution is achieved as disclosed in French Patent No. 985,174 for example.
Furthermore, French Patent Application Nos. 86 07 849, 86 07 850, 86 07 851 and 86 07 852, disclose skis whose lateral surfaces or edges of the skis have variable inclinations that vary length-wise along the ski. The contact of these edges with the snow achieves desirable results, particularly during the execution of turns.
Conventional skis generally have a composite structure in which different materials are combined in a manner such that each of the materials operates in an optimal fashion taking into account the distribution of the mechanical stresses in the skis. The composite structure comprises resistance or reinforcing elements or layers formed from material having a high mechanical resistance to strain and a substantial rigidity so as to resist the flexional and torsional stresses produced in a ski during its use. The conventional structure further includes filler elements and absorption elements.
The two principle modern composite structures currently finding wide scale application in skis are the so-called casing structure and sandwich structure. In a typical casing structure, such as described in French Patent No. 985,174 and FIG. 3 of French patent No. 1,124,600, a ski comprises an internal core made of cellular material which may be partially hollow, and resistance elements surrounding the core in the form of layers that constitute a casing for the core.
In a typical sandwich structure, such as described in U.S. Pat. No. 4,405,149, a ski comprises a central core formed from cellular material which can be partially hollow, and reinforcements on its upper and lower surfaces formed by resistance layers having resistance and rigidity properties greater than those of the core itself. Typically, discontinuous strips of stressed viscoelastic material are bonded to the core along two or three separate, longitudinally spaced zones. At least one of these zones is near the spatula of the ski, and another of the zones is located adjacent the binding zone.
Swiss Patent No. 525,012 discloses longitudinal strips formed of viscoelastic material bonded to the upper surface of the ski to form a sandwich structure.
In all known skis utilizing a sandwich construction in which viscoelastic strips are the shock absorption elements, the strips have a uniform width along their entire length. When the strips are positioned substantially over the entire length of a ski, it has been found that skiing comfort is increased, but that the gripping and holding power of the ski during turning maneuvers are reduced. In efforts to solve this problem, it has been proposed to limit the length of the shock absorber to the front half of a ski, i.e., to the zone located between the spatula and the binding zone. Such an expedient, however, appears to provide no advantage over a construction in which the shock absorber extends over the entire length of the ski. Finally, where the strip is segmented or divided into a plurality of separate segments, as described in U.S. Pat. No. 4,405,149, the shock absorption effect is reduced, and the influence of the segments becomes practically negligible at the vibration frequencies produced in a ski in normal use when a boot is attached to the ski by a binding.
Further, in conventional skis using a sandwich construction, the shock absorption element constitutes a supplemental element which complicates the manufacture of the ski and substantially increases its cost.
An object of the present invention is, therefore, to provide a new and improved ski which avoids the disadvantages of known ski structures and has improved shock absorption that increases the comfort of the user and improve technical performance. The most troublesome vibrations that appear when traditional skis are used are sufficiently reduced by the present structure so as to be imperceptible. Simultaneously, the absence of vibration in the same range of frequencies produces a substantial increase in the gripping effect of the ski in ice or snow, in its stability on bumps, in its stability in turning, and, finally, during sliding.
Another object of the present invention is to provide a ski having a sandwich or casing structure capable of conferring to the body of the ski, shock absorption properties at longitudinal locations along the length of the ski which are functionally related to the longitudinal locations.
Another object of the present invention is to provide a ski that has shock absorption properties that vary longitudinally along the ski in order to provide a ski having a desired homogeneity of both structure and behavior, and a good distribution of reactions along the length of the ski, thereby providing a user with a desired comfort level and uniformity in reaction of the ski to stresses.
Another object of the present invention is to provide a ski having both improved shock absorption properties and improved snow reaction properties.